The present invention relates to the filtration devices used in selective catalytic reduction (SCR) systems. An SCR system is a pollution-control system which reduces emissions of nitrogen oxides (NOx), making it possible to comply with the Euro 6 standard in NOx emission limits. Various SCR technologies have been developed, based on solutions of urea. Injecting urea into the exhaust allows reduction of nitrogen oxides NOx using catalysts in the presence of oxygen. The aqueous solution containing 32% urea is the eutectic aqueous solution and defines the standard reducing agent referred to as AUS32, AdBlue®, or DEF (Diesel Exhaust Fluid). However, this eutectic aqueous solution suffers from problems which increase the complexity of installing it, such as, amongst other things, its −11° C. freezing point, which means that solutions such as heating the aqueous liquid so that the SCR system remains functional have been researched. There is another aqueous solution made up of urea and ammonium formate the freezing point of which is at −30° C. Heating solutions have been proposed for solving the problem of a −11° C. freezing point, such as in-built heating elements (FR2916188). For its information, the control logic conventionally uses the temperature information to trigger the heating of the aqueous solution. In addition, because the solutions may contain impurities and the freezing point values may range from −11° C. to 0° C., the control logic has therefore to actuate the heating up to 0° C. in order to ensure the switch from the solid phase to the liquid phase. WO 2013/178352 discloses the use of a pressure sensor arranged in the filter and allowing indirect determination of variations in volume.
We are going to set out the invention which proposes a device for triggering the system for heating the aqueous solution when the aqueous solution is in the solid phase.